This invention relates to a release agent having excellent running and lubricating properties, which can be used for a low speed injection casting such as squeeze casting.
A low speed injection casting process with a slow casting speed of a molten material may produce cast products with a high strength because it hardly entraps of the air or gas in a die. Therefore, the low speed injection casting has been adopted for manufacturing safety parts for automobile, which are progressively being made of aluminum from the standpoint of weight saving.
The low speed injection casting requires good lubricating property, because a molten material is easily cooled and solidified prior to reaching the end of a die owing to its low casting speed, and should be pushed by a plunger or a localized pressure pin for preventing shrinkage cavity.
The release agents hitherto used for low speed injection casting are graphite (JP-A 5-7978), a dispersion of white inorganic powders such as talc and mica or a combination of said dispersion of inorganic powders with a wax emulsion (JP-A 9-66340), and an aqueous suspension of granules of the release agent composed of a porous synthetic silicic acid compound having a specific surface area of 40 m2/g or more (JP-A 6-114494).
However, in regard to the prior art as mentioned above, graphite has the problem that it has a good lubricating property but may cause pollution of surrounding working environment because of its black color. On the other hand, the inorganic powder system may provide a favorable working environment, but it has the problem that the lubricating property may be insufficient and sediment may be easily formed over a die, which has difficulty in cleanability, so that it may take a prolonged time to polish a die, resulting in lowered productivity.
This invention is to solve the above-mentioned problems and an object of this invention is to provide a release agent for low speed casting which does not cause any pollution of working environment and shows superior running property and lubricating property with an excellent cleanability of a die.
The low speed injection casting (or die casting) as used herein includes squeeze casting, die casting with laminar flow charging, and vertical pressure casting, and refers to a casting process wherein a molten material is cast into a die at a low speed (0.05-2.00 m/s) and then solidified under elevated pressure (100-1500 kg/cm2).
We have made our studies in order to achieve the above object and found out that the most excellent is an aqueous release agent which comprises an inorganic lubricant, spherical resin particles having an average particle size of 0.1-10 xcexcm, an organic carboxylic acid metal salt and water, upon which this invention has been completed.
This invention is directed to an aqueous release agent for a low speed injection die casting, which comprises as main components an inorganic lubricant, spherical resin particles having an average particle size of 0.1-10 xcexcm, an organic carboxylic acid metal salt and water.
The invention is also directed to the said release agent, which comprises 100 parts by weight of said inorganic lubricant, 5-100 parts by weight of said spherical resin particles having an average particle size of 0.1-10 xcexcm, 5-100 parts by weight of said organic carboxylic acid metal salt and 100-1000 parts by weight of water.
The invention is further directed to the said release agent characterized in that said spherical particles are in the form of an aqueous dispersion of fine particles of a polyolefin.
The invention is further directed to the said release agent characterized in that said inorganic lubricant is at least one selected from the group consisting of talc, kaolin, mica and boron nitride.
The invention is further directed to the said release agent characterized in that said organic carboxylic acid metal salt is at least one selected from the group consisting of sodium adipate, sodium isophthalate and sodium tetrahydrophthalate.
Moreover, the invention is directed to the said release agent characterized in that said inorganic lubricant is a lubricant having a flake lamellar structure and an average particle size of 1-10 xcexcm.
This invention will be illustrated in detail hereinafter. The release agent according to this invention comprises as the essential components the inorganic lubricant, spherical resin particles, organic carboxylic acid metal salt and water as explained below.
(1) Inorganic Lubricant
The inorganic lubricant includes powdery talc, kaolin, mica and boron nitride, which may be used alone or in combination of the two or more. In particular, preferable is the lubricant such as talc, which has an average particle size of 0.1-20 xcexcm, preferably 1-10 xcexcm and a flake lamellar structure. The lubricant of the said structure makes it possible for the release agent to form a film wherein spherical resin particles are incorporated between the layers of the inorganic powdery lubricant having a flake lamellar structure, and therefore exceptionally improves the lubricating property as compared with the inorganic lubricant itself.
(2) Spherical Resin Particles
The resin particles to be used may be a resin in the form of spherical fine particles having an average particle size of 0.1-10 xcexcm, preferably 0.5-5 xcexcm. Even in the case of fine particles having an average particle size of not more than 0.1 xcexcm or non-spherical particles, the lubricating property of flake lubricant such as talc may be improved, but not so significantly. As such spherical resin particles, an aqueous dispersion of fine particles of a polyolefin may be preferably used. The aqueous dispersion is prepared, for example, according to the method described in JP-A 5-156028, which comprises preparing a polyolefin molten mixture composed of an olefinic polymer and an olefinic polymer containing an unsaturated carboxylic acid, and then dispersing the mixture in an alkaline water under stirring at a high speed. The aqueous dispersion of spherical polyolefin fine particles having an average particle size of 0.1-10 xcexcm may also be commercially available as xe2x80x9cCHEMIPEARLxe2x80x9d (Trade name, manufactured by Mitsui Chemicals, Inc.).
(3) Organic Carboxylic Acid Metal Salt
Blending of the organic carboxylic acid metal salt may further improve the lubricating property and provide a coating film of the release agent with hydrophilic nature and an improved elimination of the release agent sedimented over a die.
The preferable organic carboxylic acid metal salt includes alkali metal salts such as sodium salts and potassium salts of adipic acid, sebacic acid, dodecanedicarboxylic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, trimellitic acid, pyromellitic acid, maleic acid, succinic acid and the like, and they may be used alone or in combination thereof. In particular, sodium adipate, sodium isophthalate and sodium tetrahydrophthalate are preferable in view of lubricating property.
(4) Water
Ordinary tap water may be used, but ion-exchanged water may be preferably used.
(5) Other Components
If necessary, hydroxymethyl cellulose, for example, may be blended in order to prevent sedimentation of the release agent or to accomplish thickening. In this case, it may be preferably used at approximately 10 parts by weight per 100 parts by weight of the inorganic lubricant.
(6) Amounts of the Components to be Blended and Preparation of Materials for Release Agent
The materials for the present release agent comprise the powdery inorganic lubricant, spherical resin particles, organic carboxylic acid metal salt and water as main components. The amounts of the components to be blended are 100 parts by weight of the inorganic lubricant, 5-100 parts by weight, preferably 10-50 parts by weight of the spherical resin particles, 5-100 parts by weight, preferably 10-50 parts by weight of the organic carboxylic acid metal salt and 100-1000 parts by weight of water.
The materials are to be processed using a high-speed stirrer and the like.
(7) When the Release Agent of this Invention is to be Applied, It may be 5-50-Fold Diluted with Water and then Spray-Coated, for Example, to Form a Uniform Film of the Release Agent on the Die Surface.
This invention will be illustrated in greater detail on the basis of the following examples, but this invention is not to be limited thereto.
Raw Materials
(1) Inorganic Lubricant
Talc: LMS-200 (Tsuchiya Kaolin, average particle size of 1.5-1.8 xcexcm)
(2) Resin Particles
Spherical polyolefin 1: xe2x80x9cCHEMIPEARL W-300 (Trade name)xe2x80x9d manufactured by Mitsui Chemicals, Inc. (Low molecular weight polyolefin, solid content of 40%, particle size of 3 xcexcm). 
Spherical polyolefin 2: xe2x80x9cCHEMIPEARL M-200 (Trade name)xe2x80x9d manufactured by Mitsui Chemicals, Inc. (Low density polyolefin, solid content of 40%, particle size of 6 xcexcm).
Spherical polyolefin 3: xe2x80x9cCHEMIPEARL v-300 (Trade name)xe2x80x9d manufactured by Mitsui Chemicals, Inc. (Vinyl acetate copolymerized polyolefin, solid content of 40%, particle size of 6 xcexcm).
Spherical polyolefin 4: xe2x80x9cCHEMIPEARL A-100 (Trade name)xe2x80x9d manufactured by Mitsui Chemicals, Inc. (Thermoplastic elastomer, solid content of 40%, particle size of 4 xcexcm).
Spherical polyolefin 5: xe2x80x9cCHEMIPEARL S-300 (Trade name)xe2x80x9d manufactured by Mitsui Chemicals, Inc. (Ionomer, solid content of 35%, particle size of 0.5 xcexcm).
Each of the above resins was added so as to give a solid content of 5 parts. The particle size was a numerical value as measured by means of Coulter counter.
Polyethylene wax: xe2x80x9c629xe2x80x9d (manufactured by Allied Signal Inc.) was formed to an emulsion with a wax content of 20% using an addition product of a higher alcohol of 12 carbon atoms to 9 moles of ethylene oxide (particle size of 0.1 xcexcm). It was incorporated in such an amount that a wax content should be 5 parts.
(3) Organic Carboxylic Acid Metal Salt
Sodium adipate, sodium isophthalate and sodium tetrahydrophthalate were used.
(4) Other Components
An addition product of a higher alcohol of 12 carbon atoms to 9 moles of ethylene oxide was used as a surfactant.
Hydroxyethyl cellulose (xe2x80x9cHEC DAICEL SP-200xe2x80x9d (Trade name), manufactured by Daicel Chemical Industries, Ltd.) was used as an anti-settling agent.
Evaluation Method
(1) Lubricating Property
The lubricating property of films of the release agent was tested according to the ring compression method used for evaluation of lubricating agents for plastic processing, and evaluated with the friction coefficient thus obtained. The die had a dimension of a diameter 100 mmxc3x97a thickness 10 mm and a material of SKD61. Two dies were used for the test. The die was heated to about 200xc2x0 C. and 10 ml of the sample 30-fold diluted with water was spray-coated onto one side of the die to form a uniform film. The aluminum ring test piece (material of A5052, outer diameter 54 mmxc3x97inner diameter 27 mmxc3x97height 18 mm) preheated to about 500xc2x0 C. was interposed between the film surfaces of the two dies and then compressed at a compression rate of 50% by a 100-ton oil press. The friction coefficient was calculated from the compression rate and change rate in inner diameter of the test piece after compressed.
(2) Die Cleanability
The dies used for the above lubricating property test (1) were softly rubbed with a gauge dipped in water, and evaluated based on the amount of eliminating of the film of the release agent over the die.
A: Little release agent film remained
B: Release agent film slightly remained
C: Release agent film considerably remained